WASHINGTON — Environmental Protection Agency Administrator Scott Pruitt’s phones have been ringing off the hook since he questioned the link between human activity and climate change.

The calls to Pruitt’s main line, 202-564-4700, reached such a high volume by Friday that agency officials created an impromptu call center, according to three agency employees. The officials asked for anonymity out of fear of retaliation.

By Saturday morning calls went straight to voicemail, which was full and did not accept messages. At least two calls received the message that the line was disconnected, but that appeared to be in error.

Before the number was disabled, interns were dispatched to answer some of the incoming calls, according to one employee. At times, calls to that number ended up going to voice mail.

EPA did not respond Friday to a request for comment.

While constituents sometimes call lawmakers in large numbers to express outrage over contentious policy issues, it is unusual for Americans to target a Cabinet official.

Pruitt’s comments on the CNBC program “Squawk Box” – that “we need to continue the debate and continue the review and the analysis” over climate change – prompted an immediate pushback from many scientists and environment groups. It also drew a rebuke from at least two of his predecessors at the EPA.

“I think that measuring with precision human activity on the climate is something very challenging to do, and there’s tremendous disagreement about the degree of impact, so no, I would not agree that it’s a primary contributor to the global warming that we see,” Pruitt said on CNBC.

The U.N. Intergovernmental Panel on Climate Change has concluded that it is “extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century” – a position reiterated on EPA’s own website.

On Friday, the National Oceanic and Atmospheric Administration announced that the level of carbon dioxide in the atmosphere rose at a record pace for the second straight year, reaching 401.5 parts per million. The two-year surge in carbon concentrations that took place in 2015 and 2016 has no precedent in the 59 years in which the agency has been tracking the level of CO2 in the atmosphere.

Despite the quick and fierce backlash to Pruitt’s comments, which put him at odds with his own agency and most governments around the globe, not everyone was so quick to criticize his views.

“If I am interpreting Pruitt’s statements correctly, I do not find anything to disagree with in what he said: we don’t know how much of recent warming can be attributed to humans,” recently retired Georgia Tech climate scientist Judith Curry, who herself has questioned the extent of the role humans play in global warming, wrote on her blog. “In my opinion, this is correct and is a healthy position for both the science and policy debates.”

There is no immediate evidence that any environmental organizations organized the deluge of calls to the new EPA administrator, but a single comment on Reddit may have helped spur the outpouring of criticism. The post outlined how Pruitt’s opponents could contact his office, writing:

“Here’s the number to call his office (EPA Office of the Administrator) to offer your feelings about Pruitt’s comments: (202) 564-4700. Script: Hi, my name is _________. I’m calling because I’m seriously concerned about Scott Pruitt’s claim that CO2 is not a major driver of climate change. The role of CO2 and humans as drivers of climate change is widely accepted among the scientific community, and I’m deeply concerned that Mr. Pruitt, as the head of the EPA, rejects scientific evidence.”

In December, the League of Conservation Voters launched a petition drive on climate change aimed at President Trump and his children. David Willett, its senior vice president for communications, said Friday that the league had not organized any sort of phone-call campaign related to Pruitt’s comments but had seen an uptick in support in the past day and a half. The organization launched an appeal Thursday focused on threats to EPA funding and had its second-biggest online fundraising day ever, Willett said, but he declined to disclose how much money was raised.

“It’s not surprising to hear people are calling after Pruitt contradicted his own agency’s science,” Willett said. “We’re seeing record-setting response rates to mobile alerts, petitions and funding appeals.”